The present invention relates to controls for steering brakes and clutches of crawler vehicles and more specifically relates to controls for sequentially effecting the disengagement of a clutch at one side of a vehicle before application of the brake on that side when only one of the brakes is being applied but acting to prevent disengagement of either clutch when both brakes are being applied simultaneously. Exemplary of prior art steering controls, which operate in the manner just described, are the controls described in U.S. Pat. No. 3,494,449, granted on Feb. 10, 1970; U.S. Pat. No. Re. 29,293, granted on July 5, 1977 and U.S. Pat. No. 3,899,058, granted on Aug. 12, 1977.
Heretofore, prior art steering controls of the above-described type have suffered from one or more of the drawbacks of having relatively complex linkages and/or valving, of lacking compactness, and of lacking the ability to automatically effect engagement of the brakes in response to the loss of hydraulic system pressure as would happen in the event of a failure in some components of the system or in the event of the vehicle engine stalling, for example.